November 1, 2010

Scientists Confirm China Was Birthplace Of Plague

A new study tracking the DNA signature of the plague has found that the deadly disease first broke out in China more than 2,600 years ago before making its way to Europe via Central Asia's "Silk Road" trade route.

The findings prove many suspicions about the long-believed Chinese origins of the plague, which killed nearly a third of Europeans during the Middle Ages.

Scientists from around the world sequenced 17 strains of Y. pestis, connecting them as pathogens that mutated from a common ancestor.

France's Museum of Natural History said the results of the sequencing indicate that the "plague appeared in China more than 2,600 years ago."

It then spread into Western Europe along the Silk Road, more than 600 years ago, and then spread to Africa, most likely from an expedition led by Chinese seaman Zhang He during the 15th century, the museum said.

The disease arrived in the United States through the ports of San Francisco and Los Angeles from China via Hawaii in the late 19th century, according to molecular evidence.

"The work highlights specific mutations in the bacterium showing how the germ evolved within given geographical regions," the museum said in a press release. "But it demonstrates in particular that successive epidemic waves originated as a whole in Central Asia and China."

The study could be useful for tracking the routes and origins of other bacterium, such as anthrax and tuberculosis, it added.

Y. pestis originated in rodents, especially rats. The bacterium was transmitted via fleas who fed on infected animals than passed it on to humans when they subsequently fed on them. The resulting infection of the lymph gland was called bubonic plague.

Pneumonic plague, which is less common, is actually more virulent. It is transmitted human to human when a person with bubonic plague transmit's the bacteria through airborne droplets in coughs and sneezes.

The study, led by Mark Achtman of the University College Cork in Ireland, included scientists from Britain, China, France, Germany, Madagascar and the United States. The findings were published online Sunday by the journal Nature Genetics.


Image 1: Scanning electron micrograph depicting a mass of Yersinia pestis bacteria (the cause of bubonic plague) in the foregut of the flea vector. Credit: Rocky Mountain Laboratories, NIAID, NIH

Image 2: Routes of transmission of plague from Hong Kong since 1894. Colored arrows indicate distinct historical routes of transmission by multiple closely related lineages within Yersinia pestis 1.ORI, the history of which is distinguished by lineage-specific and country-specific nucleotides (mutations). 1.ORI1 spread to India (inset) and also to the United States via Hawaii. 1.ORI3 also spread to India (inset) and then to Madagascar and finally to Turkey. 1.ORI2 spread globally through radiations ii (VietNam), iii (West Africa), iv and vii (South Africa), v (South America), viii (South America via Europe). 1.ORI2 also seems to have spread  by land from China to Vietnam and Burma (inset, radiation ix).


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